Heretofore, there has been generally known a catalyst component containing a titanium compound as a catalyst for homopolymerization of olefins such as ethylene and for copolymerization of ethylene and alpha-olefin. In order to increase the activity of this catalyst, or in order to increase the catalytic efficiency per unit quantity of titanium in the catalyst component, several attempts have been made to contact a titanium compound with a treated metal compound such as a magnesium compound.
Such attempts include a process in which an oxygen-containing compound of magnesium is reacted with a halogenating agent and then the reaction product is contacted with a titanium halide (Japanese Patent Laid-open No. 8395/1972), a process in which a hydroxyl group-containing magnesium compound and a magnesium alkoxide are copulverized and then the resulting product is contacted with a titanium halide (Japanese Patent Publication No. 34098/1971), a process in which a magnesium halide, a magnesium alkoxide, and a titanium halide are copulverized (Japanese Patent Laid-open No. 80383/1976), and a process in which a magnesium halide and a titanium compound are copulverized and then the resulting product is reacted with a titanium tetrahalide (Japanese Patent Laid-open No. 151011/1980).
The polymerization catalyst prepared from a catalyst component obtained by the above-mentioned process is improved in catalytic activity; but there are still some problems unsolved. They are: (1) the resulting polymer is low in bulk density and this decreases the productivity of the polymerization reactor; (2) the catalytic activity considerably decreases where polymerization takes a long time; (3) hydrogen as a molecular weight modifier becomes less effective, and a high hydrogen partial pressure or a high polymerization temperature is required if it is necessary to increase the melt index of the polymer; (4) the reactivity is low in copolymerization with other olefin as a comonomer, and a high comonomer concentration is required; and (5) copolymers cannot be produced in high yields, because the bulk density of copolymer decreases and solvent-soluble low-molecular weight polymer is formed in large quantities, when the comonomer content in copolymer is increased to lower the density of copolymer.